So, for you, seeing a spider is a trigger for continuously watching, and edging your way around your living room. From the sofa, to the floor, to as far out the door as you can possibly get, spiders for you mean time to be alert and watch their every move.
The aim of this set of exercises is for you to be able to try and calmly coexist with spiders, knowing that there is one near you. It may sound like an impossible nightmare, but you can do it and you'll feel much better after!
The first step is to try to work out why you feel the need to constantly monitor what spiders are up to. For some people, the answer is as simple as "It means I can run if they come too close". However, others may have been misled by scary facts about spiders, and so their reasoning may be more like "I stay more than 2 feet away in case the spider jumps at me".
The key here is for you to go out to a spot you like. For some it may be a nice, quiet spot, like a library or a local park. Others may prefer active social settings, such as a coffee shop or a gym. Pick whatever place makes you feel comfortable and allows you to think clearly. What are you going to be thinking about? Spiders.
The idea here is for you to think about why it is you watch the spider, and what you are watching for. Maybe you don't like their leg movements, or perhaps you imagine something terrible that would happen if a spider comes close. Think about these things, and then, write them down. Keep your notes handy, as they will come into play during the next step.